This invention relates generally to an array for receiving wave energy and particularly to an array for providing nearly optimum performance at a given low frequency while supporting operation at much higher frequencies.
Systems containing arrays of transducers such as linear or planar arrays used in underwater sonar systems are well-known. Conventional sonar systems are hampered by having narrow frequency bandwidths.
The fundamental difficulty in designing an array that must function at two widely-spaced frequencies is that an array with the customary element spacing of approximately one half wavelength designed for the higher frequency would have very low array gain at the lower frequency. A conventional low-frequency design would be aliased at the higher frequency. When an array is aliased, it is impossible to determine from which of several directions signals are arriving. The usual approach to the problem of designing an array that must have widely-spaced operating frequencies is to dedicate a subset of the array elements to each frequency, which is, in effect, providing separate arrays.